The transfer of data and downloading of applications from personal computers to portable computing devices has become commonplace. The communication between such devices can be over a cable linking their serial/parallel ports, via modems that use the telephone system, by display screen modulation, over an infrared (IR) data link, or through a radio frequency (RF) transmission. Floppy disks or other types of non-volatile transferable storage such as compact disk-read only memory (CD-ROM) disks can alternatively be used to load application programs into a portable computing device.
A new type of portable computing device is being developed that will enable personal information management (PIM) functions to be combined with portable communication functions. A first commercial embodiment of this new technology will likely be a pager that includes PIM capabilities. In addition to receiving conventional page messages over a standard paging channel, this device, which is referred to as "Nomad" will maintain data such as schedules, addresses, phone numbers, contacts, etc. Furthermore, it will have a limited processing capability so that small software applications can be executed by it. These software applications, which are called "applets" because of their small size, can be downloaded from a personal computer or other source into a memory of the Nomad pager over the RF paging channel or via an IR data link. The capabilities of Nomad are clearly not limited to a combination pager and PIM. It is expected that many of the features and functions of Nomad, including the ability to run small application programs, will be incorporated in other portable devices, such as cell phones, watches, pocket organizers, etc.
One of the problems that must be addressed as this new technology becomes available is the potential for application software to be downloaded that does not behave properly and thus, causes problems in the operation of the portable device on which the software is executed. Since an applet can be downloaded to Nomad as a paging object without being requested by the user, the user may not even know the source of an applet. It will therefore be important to provide a mechanism to prevent improperly written applets from executing on Nomad, since such software could adversely affect the normal operation of the device or cause loss of important data stored in the device. Thus, it will be apparent that some technique should be employed to discourage or prevent improperly written application software from executing on the device. Consumers will likely demand that only application software from an approved source will be able to execute on the device to ensure that the software is properly written and does not cause problems when executed.